Oxygen abundance in the Sloan Digital Sky Survey

¹ Center for Astrophysics, University of Science and Technology of China, 230026, PR China e-mail: sfemail@mail.ustc.edu.cn
² National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received: 16 November 2005
Accepted: 22 February 2006

Abstract

Aims. To assess the possible systematic differences among different oxygen abundance indicators and understand the origin of nitrogen and the stars responsible for nitrogen production, we present two samples of galaxies from the Sloan Digital Sky Survey (SDSS) spectroscopic observations, data release 3.

Methods. The electron temperatures (T_e) of 225 galaxies are calculated with the photoionized model and T_e of 3997 galaxies are calculated with an empirical method. The oxygen abundances from the T_e methods of the two samples are determined reliably. The oxygen abundances from a strong line metallicity indicator, such as R₂₃, P, , and , are also calculated. We compared oxygen abundances of galaxies obtained with the T_e method, R₂₃ method, P method , method, and method.

Results.The oxygen abundances derived with the T_e method are systematically lower by ~0.2 dex than those derived with the R₂₃ method, consistent with previous studies based on region samples. No clear offset for oxygen abundance was found between T_e metallicity and P, and metallicity. When we studied the relation between N/O and O/H, we found that in the metallicity regime of , the large scatter of the relation can be explained by the contribution of small mass stars to the production of nitrogen. In the high metallicity regime, , nitrogen is primarily a secondary element produced by stars of all masses.